So this morning I went on recreation.gov and saw there were 10 Whitney exits available at the farthest date out AND a South Lake entry for 7 days prior. This is Aug 14 to Aug 20, which would be 7 days of hiking. I took the pass and have the confirmation, so at least I have SOMETHING reserved now.

I don't think I can do 100 miles including Whitney summit in 7 days, I would rather take 10 days. What are my options to modify this pass with a later exit? I will keep watching for a more ideal setup with a 10 day window and then cancel this 7 day reservation, but if that doesn't happen, is my only hope a walk-up?

Edit: I see now I can edit my reservation but I can only edit the start day, not the end day. So maybe if I keep watching I'll find South Lake open up again on Aug 11 which would be ideal.